How to properly texture sculpted model
So you need to know the basics of UV unwrapping .

UV unwrapping

https://www.youtube.com/watch?v=f2-FfB9kRmE

You also need to know how to texture , You dont need to texture it , you can also use materials but it isnt the best idea if you arent using it only for rendering :

https://www.youtube.com/watch?v=thYHF0282cE

Also be sure to look at lots of references and watch how other people do it :

https://www.youtube.com/watch?v=C3r2T7xU9Kw

there is also Clone painting , Shown in this video

https://www.youtube.com/watch?v=p4ngVoGIj1Q

And since you are beginner you might want to take a look at  basic texturing :

https://www.youtube.com/watch?v=SwpwzHPtqMc